Selecting a External Pond Pump
While the most popular pump for pond applications is usually a submersible pond pump... the often overlooked is the external pond pump.
While the mag drive pond pumps and direct-driven are submersible the external pond pumps are non-submersible and are actually installed outside of the pond water. Being located outside of the pond is the reason they were coined the term "external". They can be an excellent choice in any pond or waterfall installation.
What Actually Makes Up a External Pond Pump
The types and the features on these pumps may be slightly different but they are basically the same. A pump that is not apart of the water feature. In a basic pond skimmer you install a submersible mag drive pond pump. The same goes for pond-less waterfall basins, etc. With external applications it can also include pulling water from bottom drains in koi ponds, pushing massive flow for large waterfalls, formal decorative fountains, pond filtration and circulation, or other situations that a submersible direct drive pond pump (even more powerful than most mag drives) is not the best choice.
Magnetic Couples Asynchronous External Pond Pump
A magnetic coupled asynchronous pump is a type of external out of pond pump. They can be used as a submersible and also external pump that is in-line and features tubing intakes and also outlets. So they are kind a best of both worlds being submersible and external.
Most of the time they are used on small ponds, wall fountains, and tank water features. We think that this kind of pump may be the next big thing in the pond pump world. New technologies are rapidly improving these pumps and it will be exciting to see what the future holds for them in external pump applications.
Centrifugal External Pond Pumps
The more commonly recognized external out-of-pond pumps is the centrifugal pump. These are what most hardcore koi pond hobbists are familar with. They range in flow from as little as 2000 GPH all the way to huge 3 HP external pumps that can have water flow ranges in the 10,000+ GPH. Most pump manufactures divide these pumps into a couple different catagories. It can be confusing, but once you know what you're looking for it is pretty simple.
Centrifugal external water feature pumps are usually spit into either flooded suction pumps, or they are self priming.
After that they are divided into low head to high flow, or high flow to high head and can be designed to work with 115v or 230 volts. Some pumps even can work on either electrical voltage. They can also be multiple speeds, or just a single speed. As you can see it can get pretty confusing when deciding on what is the right pump for your water feature.
Low Head or High?
When you get into trying to figure out if a low or high head pump is needed you need to look at how tall your water feature is.
For example - If you are creating a 3 or 4 foot tall waterfall, or if you are going to use a pressurized pond filter you can usually get away with a pump that has low head.
However if you have a water feature that has a 25' high waterfall and it is a far distance from the pump to the waterfall you are going to be required to use a high-head pump.
Calculate Your Total Dynamic Head
Before doing anything else you are going to need to calculate your total dynamic head to figure out which pump to use. To figure out the total dynamic head calculate the height of your water feature, feet of pond pipe water will be pushing through, inside diameter (ID) of pipe, what kind and how many pond fittings are installed in the pipe. You can find calculators online to make is easy. Tyr this TDH online calculator.
After you have that number you can figure out the GPH of water flow you are going to need at the total dynamic head. Most all major pond manufactures will have a chart showing GPH at certain head heights/pressures. This is important because if you choose the wrong external pump for pond it can waster electricity, or can cause pump failure.
So lets look at an example to help make this make more sense. Say your pond installation called for a TDH of 15 feet and you want a water flow of 5,000 GPH. Techically you could use as external high head pond pump. But, that is not your best choice. The pump with high head will use more electricity than if you chose a low-head pump. You could be wasting money each year just from this simple mistake.
Also, the external pump with high head may end up with a reduced lifespan due to not having enough backpressure during operation. Proper pressure is important and if you don't have enough it can create cavitation in the pump imepellor chamber and overheat the pumps motor.
Lets dig a little deeper into this example pump application. Say in the above example specs we are looking at 2 external pumps that are both rated at 8,000 GPH max flow. But, one external pump is a "low head" external pump, and the other one is a "high head" external pump.
You could use the Easy Pro EX8800 which is low head and has a mx flow of 8200 GPH at 15 feet head will pump out 5040 GPH flow. On the flip side is the EasyPro EX8500 which is high head with a max 8500 GPH flow and when you look at the head chart at 20 feet of head it can still pump 6960 GPH! But here is where the electricity comes into play. If you installed the high head EX8500 pump it would use 1385 watts. Where the low head EX-8800 would only consume 449 watts. If we plug that into some formulas the long and short of it is that at average electrical rates the high head pump will use $616.85 greater dollars than a low head pump would in the same application.
Another thing to keep in mind is if you used the high head external pump in our above example you would have to restrict the water flow in order to have enough backpressure on the pump to help stop cavitation which could cause premature pump wear or failure.
But, if say you were doing a pond installation and the total dynamic head was 30 feet.. you could not use the low head pump because at that pressure it would not work at all. Where the higher head EX8500 would still be cranking out 6,000 GPH of flow.
Different Voltages You Can Use
You can usually use 115 volt or 230 volts on most external pond pumps. All it takes is a simple modification and you are ready to go. Small external pumps most likely only use 115v though.. and really large external pond pumps will most likely only use 230 volts beacause of the demands placed on the pumps.
Many people think that running the 230 volts pumps will save money in electrical costs. But, in the long run most of the time the cost is the same between 115 and 230.
You must also keep in mind that if you have a water feature in your backyard and thinking about using 230 volts you may need to use different installations methods than if you were going to use 115. Here is where a qualitfied electrician and your local building codes come into play. So keep this in mind when selecting a pump.
Large external pumps can benefit from 230v though. But, again you may need to upgrade electrical installation, material, and labor costs.. so the small savings in electricity may get swallowed up in other costs and not worth the effort to switch it out.
Self-Priming and Flooded Suction External Pumps
When looking at external pond pumps you will see self-priming and flooded suction pumps. The decision should be matched to the application.
Flooded suction pumps need to be placed at water level, or below in the water feature so it will have a constant flow of water. Because of this most pond builders place the flooded suction external pumps in a well or sump area. An important tip is to make sure the area is big enough for air for circulation around the pump. Ventalation in the pump chamber will help the pump last longer. Some will even go so far to install a small fan to stop overheating. This may seem like a little more work than a submersible pond pump, but it will pay off as some external pumps can last for 10 years if properly cared for.
If you do your pump installation at water level it is reccomended that you install a check valve with its tubing below the water line to help the pump stay primed when the pump is shut off. This way you will not need to hand prime it.
Self priming external pumps can give you the freedom to install the pump above water level. The pump will suck water to it. So when looking at your water feature design you can compare whether it is possible to locate the pump at, or below grade. If it is a flooded suction pump will work, if not then a self priming pump may work perfect.
But, you still have to prime both flooded suction and self-priming for the first time you turn the pump on. You can install a check valve fitting, and the filling of the pond tubing, or leaf basket.. or priming pot as there are sometimes called can prime your pump for the first time.
Speeds of External Pumps
The last thing you will need to figure out is speed. Some pump manufacturers have a simple switch that runs the pump at a low or high speed. The setting of the pump will determine the GPH flow that the pump will make. You would want to choose this sort of pump when running at a lower speed to produce the desired flow, but you also want higher flows at certain times.
You may want the higher flows if your having a party and want a more dramatic waterfall to really show off your water feature. You could also use the setting to backwash a pond bio filter to provide a little extra cleaning power.
But, you need to keep in mind that running the pump at the higher speed is going to need more resources and cost more money in electricity. With certain pumps you could double the speed with the setting, but it will eat up more than 4 times the amount of electricity!
That may not be of concern if you are running the pump at the low speed setting 95% of the time and conserving energy. But keep in mind if your having a pond party and your pump is located next to a patio, etc. where people will be standing.. as the power of the pump increases so will the noise.
Control Speed and Protect the Pump With VCP
Just like the 2 speed pumps variable speed control panels are a great way to reduce the costs of operating a big external pump. It can also extend the life of your pump with the help fo "soft" stops and starts on the motor.
They work great for adjusting the flow for a party just like the dual speeds, but can also instantly shut the power off in the case of a fault, or short.
While variable speed control panels are costly the benefits can out weigh the costs on large external installations in time.
Thoughts to Consider
On thing to mention is that you should NOT use a external pool pump with pond use. It will be both costly to operate and most likely burn out very quickly. This is due to backpressure, pump designs, etc.
You should always install a check valve fitting with external pumps just as you would with mag drive pond pumps or direct drive pond pumps that are submersible. Using a check valve keeps the water locked into place and makes it easier to prime.
Leaf traps/baskets/priming pots are good to use as well. Since external pumps can not handle solids as well a submersible pond pump can it requires filtering the water before entering the pump and keeping everyting clean. They will also help maintain prime.
It is a good idea to use ball valves on each side of the tubing on the both sides of the pump to make pump removal and pump maintaence easier. It will also prevent water loss when you take the pump out.
Placement of external pond and waterfall pumps should be as close to the water supply as possible. So if you had your pump hooked into the bottom of a pond skimmer you would want to install the pump as close as you can to that pond skimmer. Long pond pipe runs make it hard for the pumps to primer and draw the water in.
When designing your water feature and selecing the correct external pump it is important to keep in mind the pipe size. Most pumps will come with a intake and outlet size.. say 2" ID, but your application may require you to choke that down to 1.5" or expand it to 3". Most of the time the larger pond tubing that is hooked up the less friction and the better the pump will run.
But one thing to keep in mind is that you should use equal to or larger tubing size on the pump intake side as the water discharge side.
Cavitating - In the article we used this term. When you hear a sound coming from a pond pump that resembles gravel spinning in the pump it is caitating. What is happening is that the pump is chewing on a froth of water and air. If this happens you will need to service the pump and check the backpressure and pump.
Conclusion on External Pumps
Picking out a external pond pump can be tough for a first timer. But, just take things one at a time and figure out what you need with your head, and research pumps on the market to see if you can find a fit. If you need any assisstance you can always contact us, or manufactures of external pond pumps for additional help.